Circuit assemblies have different components that are assembled using different manufacturing processes. One of the components often used in a circuit assembly is a metal casting, which is typically in the form of a heat sink. The heat sink is connected to other components, such as a printed circuit board (PCB). The connection between the heat sink and the PCB is typically accomplished using a wire bonding process, where the surface requirements are always high in regard to cleanliness, composition, roughness, and finish.
Wire bonding is the method by which a length of small diameter soft metal wire is attached to a compatible metallic surface without the use of solder, flux, and in some cases, with use of heat above 150 degrees Celsius. Soft metals includes Gold (Au), Copper (Cu), Silver (Ag), Aluminum (Al), and alloys such as Palladium-Silver (PdAg) and others.
Some current processes used for wire bonding on the PCB require a specific intermetallic interface between the aluminum bond and nickel phosphorus plating for solder and bonding. These processes also have various failure modes which limit the applications which the wire bonding process may be used for.
Immersion gold is a robust surface for bonding. However, contamination or imperfections in the gold may result in a non-stick condition. The failures may be the result of supplier manufacturing, shipment, or production environment, or other factors.
One type of process for polishing the surface is a diamond milling process. However, this process is expensive, and increases manufacturing costs significantly when used.
Accordingly, there exists a need for a process which provides a surface that is sufficient for wire bonding, minimizes or eliminates failures, and is cost effective.